Shields do nothing for collisions, while integrity fields can help, so long as the collision is survivable in the first place. Fewer bits lost. Plus, weapons can generate with % to pen shields. Run around without integrity fields, you're gonna run into such a foe sooner or later, and you may find yourself desiring them, when that big alien ship is punching entire cannon volleys through your shields. I speak from experience there, but I already had integrity fields. Still hurt, just fewer bits missing once the battle was over.